This invention relates to a method and a device for joining work pieces by brazing or soldering wherein an induction coil is brought to a position where it at least partly surrounds and is electromagnetically coupled to the work pieces which by means of induction are heated to a suitable temperature for the brazing or soldering operation after which a solder is fed to the soldering or brazing area.
Soldering and brazing are well-known joining methods and are used for fixing two metal parts to each other by means of the so called solder which usually is fed to the soldering or brazing area in wire or powder form. The composition of the solder differs from, and has a lower melting point than, the material in the work pieces. During the soldering or brazing operation the work piece surfaces forming the joints are heated but are never allowed to melt.
In order to achieve a bonding between the solder and the joining work piece surfaces, the surfaces must be free from oxides. Such a clean surface is usually created by a grinding operation or by applying some kind of chemical agent, a so called flux, before or during the soldering or brazing operation. The flux usually is applied as a liquid, a paste or as a powder and is sometimes mixed into the solder. When soldering or brazing in an oven it is also common to use a protective gas in order to prevent the creation of oxides.
Usually brazing and soldering are referred to as different methods where brazing is effected between 600.degree.-900.degree. and soldering below 300.degree. C. Brazing normally gives very good strength and can also be used for power transmitting joints whereas soldering gives comparatively low strength values and therefore is used primarily for sealing purposes and for electric joints.
In order to heat the work pieces, different kinds of heating means are used for the brazing as well as the soldering operation. Thus, for example, gas burners, different types of electric heating and heating in ovens are used. One often used heating method, particularly for automatic manufacturing, is the induction heating method where the work pieces are placed in a coil which is influenced by a high frequency alternating current. One example of the last mentioned method appears from swedish patent No. 8601977-5. According to this patent publication solder is fed to the work pieces after having been preheated to a suitable temperature whereby the flow out of the solder on the joining surfaces is promoted.
One difficulty when using the last mentioned method in an automatic process is that there is a need for fluxes as noted above. These fluxes must be applied manually or by providing the equipment with means by which the brazing or soldering surfaces can be dipped into the fluxes. When the flux is heated, heavy smoke from flux burn-off occurs. Sometimes flux remains in the joint which can cause joints which are not tight. Further, when the soldering or brazing has taken place there is a need for washing the joint by a so called devitrification operation.
The purpose of this invention is to achieve a method and a device which is suited for automatic production where applying the flux is facilitated and where the additional drawbacks referred to above are eliminated.